This invention relates to tools for tightening and loosening lug nuts and similar threaded members and in particular to rotatable impact wrenches.
The conventional lug wrench for adjusting such threaded members comprises a nut-engaging end piece, a shaft extending axially rearwardly therefrom and a cross member affixed transversely to the shaft to apply torque to the shaft and thereby rotate the nut. Such manual tools are only suitable for tightening and loosening lug nuts and bolts within a relatively low range of applied torque.
Most auto shops and tire dealers use pneumatic or electric lug tightening machines. Passenger car nuts are usually secured at 70-95 ft-lb torque; truck nuts may be secured at up to 450-500 ft-lb of torque. The large and numerous lug nuts on trucks, farm implements and similar large vehicles are usually tightened by such lug tightening machines. When on the road or in the field, the truck driver or farmer typically has no access to or power for such powered lug machines. Such person is often unable to loosen machine tightened nuts or bolts, especially large, highly-torqued ones, with a conventional lug wrench. Rusted nuts and bolts are likewise difficult to remove.
Various modifications of the conventional manual tool have been tried to overcome this problem.
A long cross member will provide greater torque by increasing the lever arm of the physically applied force. To do so, an extension or "cheater pipe" is applied to one of the cross members of a conventional lug wrench. Extensions of three up to six feet long are commonly used. Still, applying the weight of an adult male to the end of such an extension is sometimes not enough to loosen a stubborn lug bolt. Moreover, increasing cross member length can cause the cross member to bend under applied force. Using an extension can also apply an off-axis torque to the shaft and lug nut or bolt. Application of off-axis torque can break the bolt or the stud on to which the lug is threaded-a disastrous consequence. Providing the support necessary to direct torque about the proper axis can make the wrench too large and heavy to take conveniently on the road or into the field.
Another form of lug tool is a rotatable impact wrench as shown in Shandel U.S. Pat. No. 3,158,050. It shows a nut-engaging end piece, the central shaft extending axially rearward therefrom, and a rotary member mounted for relative rotation on the central shaft. This rotary member is positioned axially adjacent a planar flange affixed on and extending radially normal to the central shaft. The flange includes two parallel cylindrical abutments extending axially toward and overlapping the plane of rotation of the rotary member in diametrically opposed positions about the central shaft. The ends of the elongated rotary member are weighted. To loosen or tighten a nut, the user spins the rotary member in the desired direction of nut rotation. When the rotary member strikes the abutments, the angular impact is transferred to the flange, central shaft and nut. A sufficient angular impact will loosen the nut.
I have previously constructed and used a Shandel-type lug tool in which the flange and abutments were provided by a U-shaped channel member fixedly mounted on the shaft. The tool was, however, inadequate. With repeated striking, the diametrically opposed channel member flange edges would bend outward, out of the reach of the rotary member, until the tool became non-functional. A similar problem, flange and abutment bending, is likely to occur also in the Shandel tool.
Another disadvantage of Shandel-type rotary impact tools is that they are unsuitable for very large and/or stubborn or "frozen" threaded members. Highly-torqued or frozen nuts or bolts require greater applied torque or angular impact to loosen than do their smaller and less tight counterparts. Available rotational space between the abutments limits the attainable rate of rotation of the rotary member. Therefore, in practice, to provide angular momentum producing an angular impact sufficient to break free large or stubborn nuts requires increasing the moment of inertia of the rotary member. This can be done by making the impact weights heavier. Here problems arise. Increasing the moment of inertia would expedite bending of the channel member flange edges or abutments and flange, rendering such tools useless more quickly than with the lighter weights. The problem thus remains that the closer that the manual tool comes to being able to free all types of nuts, the greater the likelihood of self-destructing the tool or breaking the threaded member.
Accordingly, a need remains for a durable, manual lug tool that can loosen without breaking even large, highly-torqued or frozen lug nuts or bolts.